Erractic Idling

Hello,

I have a problem with my Volvo S40 T4 (UK 1997 model) which I hope to get
some advice on.

The car will idle very erratically after city driving. At a stand still the
engine will rev from 200rpm to 1500 rpm by itself, only way to stop is rev
the engine to 5000rpm for a while. At the same time if I
drive the car while this is happening the car will feel like it wants to go
backwards, whilst making a clicking noise from the engine. The car has been
known to stall during stand-still idling. Another thing I have noticed is
that the dash will brighten and then dim while it is rough idling.

The problem is getting worse, and I do have a warranty for the car which I
can claim on.

Any ideas? Maybe alternator?

Any suggestions would be appreciated.

 

Sounds as though it may be the idle by pass valve, this allows for engine
load change at rest, i.e. air con kicking in or putting on the heated rear
screen for example.

I may just need a clean out that said it could also be an air leak on the
induction side somewhere too.

John

 

It is a common fault and whilst everyone says it is different things, the
most common reason is a faulty ECU. If you have the A/C on, switching this
off will help it too. Mine did it when new (1998) but hasn't done it for the
past 2 years.

Just a quirk from a sometimes quirky car..........

Jose
"

 

Hi,

Thanks for the reply.

I hardly use a/c. The ecu had no fault codes when last booked for this
problem, they could not find a fault. Also the ecu had been changed when the
service light would not go out, but this did not fix that particular fault,
so they changed it back for the original ecu.

The problem can be intermittent, and never seems to happen when the dealer
has it. However with enough city driving it will show itself.

Thanks

 

I will preface this by saying I don't know anything about cars, but
our 99 V70
had an erratic, rough idle, almost to the point of stalling at
stand-still. We took it in for repair, the throttle body was cleaned,
and a cracked serpentine belt replaced. Problem solved!!

The car is now running pretty good with an exception, a loud,
sporadic cracking noise....It sounds like ice is hitting the
windshield!! This is happening about twice a day now whether I'm
turning, standing still, backing up etc... Any ideas?

Thanks!!

 

I get a sporadic cracking noise from the dash on my '91 740. It is caused by
having the heater on high. It's the plastics expanding when they get heated
up when it's cold outside. My older 740 and 240 don't do this, but I have
noticed that on the older cars the plastics are thicker with more sound
deadening material on them. IE. the inner covers on the doors on my '86 are
twice as thick as the ones on my '91, and the roof headlining is also twice
as thick. Aslo the '86 is a quieter drive than the '91.
I guess what I am saying is that the build quality of the older bricks is
better. The later ones in my limited experience have more "accountant" led
design than the older ones which have more "engineer" led design. This is
only on the plastics interior side. I think that the outer body shell is
still just as good if not better on the newer cars. My ideal would be to
find a perfect interior from say an '86 and build it into a '94 shell.
My '91 also tells me when I'm doing over 85 mph by a noise from the top of
the wind screen that sounds like someone trying to start up a set of
bagpipes. It has to be the black strip covering the top A pillar where the
windscreen meets the metal. No leaks are apparent, but one of these days I'm
going to superglue the damn thing down. At rest I can't see the problem, so
I'm going to have to overclock the wifes hairdryer and point it at the
screen to see where the noise is coming from.
Stuart.

 

Thanks Stuart. Another poster from back in April wrote about the same
noise and attributed it to the plastic too...He said the plastic on
his car was actually cracking where it met the windshield. Our car is
the same year, but I don't notice any cracks.

 

No actual cracks on mine either on my '91. My older '85 started to crack
across the top of the instrument panel, but the plastics used felt
different. The newer car seems to have thinner plastic, or the older one had
more sound deadening material stuck to the plastic. Either way, the older
car never crackled but did crack, and the newer car plastic looks better but
crackles, but only when the car is being heated up from very cold. If you
see what I mean.

Stuart